"From day one we suspected it would be very hard to write citations, because it's a judgment call."

It isn't often that lawmakers spend years shepherding legislation they know will likely not be enforced.

Yet when it came to state Rep. Ron Miller's "Safe Passing" bicycle bill — a law designed to give cyclists a buffer from drivers — that's exactly what he foresaw.

"From day one, we suspected it would be very hard to write citations, because it's a judgment call" for law enforcement, says Miller, a York Republican.

Overwhelmingly passed by the legislature and signed by Gov. Tom Corbett in February 2012, the law was celebrated as a win by many bike advocates, who have successfully lobbied 25 state governments nationwide to pass similar measures.

"The state of Pennsylvania took a huge stride toward improving our Bike Friendly State standing," declared local advocacy group Bike Pittsburgh the day after Corbett signed the legislation.

The law requires cars to allow 4 feet of space when overtaking bicycles, and to pass at a "careful and prudent reduced speed." Drivers are barred from the right or left "hook," a maneuver that cuts off bikers by turning in front of them. And bikers must "use reasonable efforts so as not to impede the normal and reasonable movement of traffic." Violating the law is a summary offense — in this case, a $25 fine.

But as in many states with safe-passing laws, enforcement in Pennsylvania has been spotty: Just 42 citations have been issued statewide since the law took effect 28 months ago, 12 of which were recorded in Allegheny County, according to a City Paper review of court data. And it's not clear if the law is having a significant effect on the number of car-related bike crashes.

"It's not being enforced to the extent it should be," Bike Pittsburgh executive director Scott Bricker says today. "After two years, you would hope that tool would be used more often."

So why have so many politicians and advocacy groups bothered to pass bike-safety laws that are often unenforced and, some argue, unenforceable?

After all, citing drivers would require officers to both witness an instance of close-passing and accurately eyeball the distance between biker and motorist.

"It's just like the cell-phone law" that bars texting and driving, explains Pittsburgh Police Cmdr. Eric Holmes, noting that it's a tough violation for officers to witness. "They want to make sure the person they're writing up has actually committed the violation. They don't want to write tickets just to write tickets."

But some advocates of the law say it's largely about educating drivers and bikers of their responsibilities, and enshrining the idea that bikes have a right to space on the road cars shouldn't violate — something that can help assign liability after a crash.

These laws "should change the overall culture," says Charles Brown, a senior researcher at the Alan M. Voorhees Transportation Center at Rutgers University. Brown, who authored a study of safe-passing laws across the country, adds that such a shift "should lead to a decrease in the number of cyclists who are injured and killed on the roadways," though nationally, he notes, "There has been little overall enforcement."

Is it working?

While there isn't total agreement on how important enforcement is to the law's success, there is consensus that the law should be evaluated based on whether it reduces the number of car-related bike crashes.

"Without a doubt, you want to see those [numbers] go down," Bike Pittsburgh's Bricker says, adding that one of the biggest reasons people avoid biking is a fear of having to occupy the same space as cars.

And while the law hasn't been rigorously enforced, some contend that education alone could reduce crash rates. PennDOT, for instance, now includes references to the 4-foot buffer in its driver's manual and test, according to PennDOT spokesperson Juliann Sheldon. And even though PennDOT has not created any signage alerting bikers or drivers to the new law, Edgar Snyder & Associates teamed up with Bike Pittsburgh on an ad campaign promoting it.

In the two years since the law took effect, however, there have not been significant variations in the number of bike-related crashes in Allegheny County or across the state, PennDOT data show.

In fact, the number of crashes statewide increased to 1,390 in 2012 (the year the law took effect) from 1,324 the previous year. The number also increased in Allegheny County during that time — from 85 to 104 crashes, though that's within what appears to be the normal five-year range (in 2013, the number slid down to 93).

But data on "rear-end" collisions — the kind of crash experts say the law is likely to target — may tell a more encouraging story. Statewide, rear-end collisions have been trending downward since 2009, with the largest decreases after the safe-passing law took effect — from a five-year high of 106 in 2010 to 65 in 2013.

And while the overall number of crashes (the vast majority involved cars) did not decline, "there's probably some truth" that the law is having an effect, says Brown, the researcher who has studied safe-passing laws.

Still, it's nearly impossible to know whether the rate of crashes is changing. Since there isn't precise data on how many people are riding and how frequently, a jump in the absolute number of crashes doesn't necessarily say much about overall bike safety.

Moreover, crashes are typically reported only if someone is transported to a hospital, or if a car needs to be towed.

"It's going to be very hard to have hard empirical data that's going to prove" the law is working, says Miller, a cyclist and the bill's prime sponsor. Still, he adds, "From my own observation, I have noticed people being much more careful while overtaking a bicyclist, so I do believe the law is having an impact."

Undercover in Austin

One police officer in Austin, Texas, is leading the charge on enforcing safe-passing laws. Armed with a pole that measures compliance with Austin's 3-foot passing law, officer Rheannon Cunningham devised an undercover sting operation, which resulted in a nearly 12-fold increase in citations — and calls from departments around the country interested in replicating her efforts.

"The cyclists always felt like the police never did anything to enforce the laws [that] were there to protect them," Cunningham explains. And if drivers "don't feel like they're going to get caught or stopped for something, they will push the envelope. They'll blow it off."

Cunningham's operation works like this: Two plainclothes police officers on unmarked bikes ride along a half-mile stretch of road that has no bike lane, but is close to popular bike routes.

Whenever a car passes within three feet — something the officers are trained to judge using the pole — they would radio a marked patrol car ahead that would pull over the offending driver. (The undercover officers recorded the encounters on bike-mounted cameras in case of challenge.)

"I didn't get the feeling that people did it on purpose," says Cunningham, who participated as an undercover officer in the operation. "There's just very poor judgment on how close they passed you."

Ironically, Cunningham says, it was the cyclists caught behind the wheel who were most indignant. "Their argument was: 'We're cyclists, we know how close we passed you,' when in fact they didn't."

Fewer than 10 people were cited in Austin between 2009 and May 2013, when the sting operation started. At least 117 people have been pulled over since, Cunningham says, and 78 of them were let off with warnings to "reinforce our message of education over purely punitive enforcement." Cited drivers were allowed to take a "defensive cycling" class to get the $175 ticket dismissed.

"It's really hard to know that the operation directly affected the outcome, but I know our collisions dropped and fatalities did not increase," Cunningham notes.

For his part, Pittsburgh's Cmdr. Holmes says the Austin model "is something to be considered." He is working on refreshing his officers on bike laws in advance of the construction of a protected bike lane Downtown on Penn Avenue.

It is unclear what the wider police bureau's position is on enforcement of bike laws. Holmes said he could not speak for the department outside his zone, and Pittsburgh police spokesperson Sonya Toler declined comment after being contacted multiple times.

Eventually, though, the law may not be enforced by humans at all, predicts Anthony Rowe, an electrical and computer engineering professor at Carnegie Mellon University.

"The assumption going in is that they're going to be mandating transponders in cars" that communicate with everything from traffic lights to other cars, says Rowe, who is part of CMU's "Safe Cyclist" project. "If cars are going to have these types of radios on them [...] they could actually communicate to and from bicycles as well."

Alerts could be built in that notify drivers if they are venturing into the 4-foot zone — in effect creating virtual bike lanes, Rowe says. And using software loaded onto a smartphones, bikers could be alerted to close-passing cars as well. Such technology, if widely adopted, "could be transformational for safety," Rowe says.

In the long run, enforcing safe-passing laws will likely become a matter of programming, Rowe says: "Once cars become autonomous" — capable of driving themselves under computer guidance — "there's no reason why they won't automatically avoid cyclists."

But in the short term, Rowe explains, the technology could generate data that shows where cars are most likely to pass within the 4-foot zone, giving police a leg up on targeted enforcement. And in the immediate future, League of American Bicyclists legal specialist Ken McLeod stresses that safe-passing laws signify a willingness among governments to grab low-hanging legislative fruit, making room for larger initiatives down the road.

"Making it clear that bicycles need and deserve space on the roadway [is] a recent phenomenon" McLeod says. "We're just starting that journey."